Imaging devices such as a film camera, a digital still camera, and a digital video camera utilize a strobe apparatus equipped with a capacitor to store chargeable and dischargeable energy.
A Japanese Patent No. 3497190 (Document 1) teaches a capacitor charging apparatus capable of securely charging a capacitor while maintaining a power supply voltage necessary for an imaging device without being influenced by the current supply capability of the power source of the imaging device.
The capacitor charging apparatus of Document 1 has a switch in the primary winding of a transformer receiving a power supply voltage. A capacitor connected to the secondary winding of the transformer is charged by the voltage generated in the secondary winding. The power supply voltage is detected by a voltage detection means during charging operation. In the event that the detected power supply voltage is higher than a predetermined voltage, the charging operation is continued until a predetermined charging voltage is obtained across the capacitor with the charging current kept at a predetermined peak level. On the other hand, in the event that the detected power supply voltage is less than a predetermined voltage during the operation, the charging operation is temporarily stopped until a sufficient power supply voltage is recovered.
Although Document 1 discloses means for controlling charging of a capacitor of a strobe apparatus in relation to the power supply voltage, it does not teach means for controlling the switch in the primary winding of a transformer.
However, in a capacitor charging apparatus for use with a strobe apparatus, it is important, from a point of charging time and power efficiency, to regulate timing of an on-time in which primary current is passed through the primary circuit of a transformer and timing of an associated off-time in which the primary current is shut off to charge the capacitor in the secondary circuit.